Cooperative transport in sea star locomotion

It is unclear how animals with radial symmetry control locomotion without a brain. Using a combination of experiments, mathematical modeling, and robotics, we tested the extent to which this control emerges in sea stars (Protoreaster nodosus) from the local control of their hundreds of feet and their mechanical interactions with the body. We discovered that these animals compensate for an experimental increase in their submerged weight by recruiting more feet that synchronize in the power stroke of the locomotor cycle during their bouncing gait. Mathematical modeling of the mechanics of a sea star replicated this response to loading without a central controller. A robotic sea star was found to similarly recruit more actuators under higher loads through purely decentralized control. These results suggest that an array of biological or engineered actuators are capable of cooperative transport where the actuators are dynamically recruited by the mechanics of the body. In particular, the body’s vertical oscillations serve to recruit feet in greater numbers to overcome the weight to propel the body forward. This form of distributed control contrasts the conventional view of animal locomotion as governed by the central nervous system and offers inspiration for the design of engineered devices with arrays of actuators. •Sea stars respond to an increased load by recruiting more tube feet•Models of mechanics demonstrate that recruitment does not require central control•A robot similarly recruits more actuators under loading purely through mechanics Po et al. use experiments, mathematical models, and a robot of locomotion in sea stars to indicate an ability to respond to variable loading without central control. These findings contrast the centralized locomotor control characteristic of cephalized animals and offer the potential to inspire the design of engineered devices.